Project Summary Although flow cytometry has become a critical tool for analyzing immune cell populations in tissues, the technique is limited to approximately 18-20 parameters due to a number of technical issues. To address those limitations, an alternative technology has been developed. This technique ? Cytometry by Time Of Flight (CyTOF) employs heavy-metal labeled probes instead of traditional fluorescent-labeled probes. In this technique, cells are nebulized into a single-cell stream before being vaporized by an argon laser, and the resulting ion cloud analyzed by time-of-flight mass spectrometry. This is a relatively mature technology, whose application has resulted in fundamental new discoveries in the biological mechanisms underlying human immune responses in cancer, infectious diseases and basic immunology. Currently, this cutting-edge technology is not readily available to the Columbia University Medical Center (CUMC) research community. While an instrument is in place at Mount Sinai School of Medicine across town, it is both fully utilized and geographically challenging for CUMC to access this equipment. Based on a prospective survey of CUMC scientists, we have identified at least 6 NIH-funded major users as well as a large number of minor users. The proposed applications are diverse, leveraging the various scientific strengths of a number of CUMC labs. Some examples include Dr. Dalla-Favera?s work on understanding the phenotype of Large B Cell Lymphoma, Dr. Donna Farber?s ongoing studies of the tissue localization of human T cells, and Dr. Syke?s investigations into the basic cellular mechanisms of allograft rejection. The leadership of CUMC is strongly supportive of the acquisition of this instrument, and will provide significant additional funds beyond those requested in the S10 application. In addition, dedicated space has been allocated within the well-established CCTI Flow Cytometry Core where the instrument will be located and managed. Overall we hypothesize that the establishment of a CyTOF instrument on the CUMC campus will be pivotal in driving new scientific insights across a number of projects and disciplines.